Solar Atmospheres of Souderton, PA, has received a new, state-of-the-art vacuum gas nitriding furnace to support an increasing demand for high-value gas nitriding. The furnace was built by sister company, Solar Manufacturing.
The front-loading furnace incorporates the latest nitriding and recipe system from Solar Manufacturing. The automated control system is useful for single stage as well as two-stage (Floe) processing. All hot zone components are made completely of graphitic materials inert to the anhydrous ammonia used during the nitriding process.
“It is the time to dare and endure.” Winston Churchill made that statement in 1940, and it is apropos today, as hopefully, many of us are coming to the end of the “stay at home” quarantine and will soon be free to roam again. It has also been said that it is during particularly difficult times where possibilities are mined and take flight. We will need those encouraging words in the days, months, and perhaps years ahead as evidenced in the latest Industrial Heating Equipment Association’s (IHEA) Executive Economic Summary. The report states, “This may well be the most distressing assessment of the U.S. (and global economy) since the recession of 2008. None of the bad news that follows will come as any surprise to anyone as we are all quite aware of the damage that has been caused by the reaction to the COVID 19 pandemic.”
The report explains the difference between the 2008-09 recession and that of 2020 – the current recession is an artificial one created by the forced shutdown of the economy. The U.S. enjoyed a robust economy and healthy job numbers at the beginning of the year. “The potential silver lining to all of this is that government … can reverse the process. The day that lockdowns are declared at an end, there will be recovery. Consumers will consume again, employers will hire again, producers will produce again. How much and how fast will be the prime questions.”
In the meantime, however, “Of the twelve indicators followed in this index, there are only four that are still trending in a positive direction and they will not be holding that distinction for long.” The durable goods numbers and factory orders numbers rose a little, but this only indicates there has been a delay in terms of industry response. The activity in the durable goods category is a lagging indicator. There has not yet been enough time for the reduction in activity to manifest in the numbers, i.e., airlines, heavy construction equipment, oil field machinery, farm equipment which have all taken major hits in decline.
Durable goods tracked a bit higher this month, however, be aware that its activity is a lagging indicator.
The summary continues, “The improvement in the transportation numbers may be a bit more realistic. There has been high demand in the parcel sector as everybody has been ordering things delivered.” The other sectors in transportation have not fared as well like ocean cargo, air freight, and the rail sector.
The transportation sector is showing some positive development.
The only other area that experienced a gain was in capacity utilization, “but that will shift as there is now considerably more slack in the system than was the case earlier.” Normally these numbers would reflect the pushes and pulls of supply and demand, but that process has been interrupted … and now almost every business has an overcapacity concern.
We are all living in a “waiting” mode anticipating the “all clear” proclamation. Then, as the summary report concludes, “Once some measure of control is achieved, the economy will be restarted, and then the focus will be on the speed of recovery.”
The report is available to IHEA member companies. For membership information and a full copy of the 12-page report, contact Anne Goyer, Executive Director of the Industrial Heating Equipment Association (IHEA). Email Anne by clicking here.
Welcome to another episode of Heat Treat Radio, a periodic podcast where Heat Treat Radio host, Doug Glenn, discusses cutting-edge topics with industry-leading personalities. Below, you can either listen to the podcast by clicking on the audio play button, or you can read an edited version of the transcript. To see a complete list of other Heat Treat Radio episodes, click here.
Audio: Heat Treat Modeling With Justin Sims
In this conversation, Heat Treat Radio host, Doug Glenn, interviews Justin Sims of DANTE Solutions about heat treat modeling. As the heat treat world moves farther way from mysterious black box processes, find out how the latest advances in heat treat simulation software can help your company model specific processes and materials in advance, leading to less guesswork and more profit.
Click the play button below to listen.
Transcript: Heat Treat Modeling With Justin Sims
The following transcript has been edited for your reading enjoyment.
We're going to talk to Justin Sims, lead engineer at DANTE Solutions, Inc., about heat treat modeling. It's a pretty interesting topic. With all the advances and sensors and computing power, the heat treat world is moving further and further away from the mysterious black box processes of yesteryear and is allowing companies to model specific processes and specific materials in advance so that there is less guesswork and more profit. DANTE provides the means by which companies can accurately predict what is going to happen to their part during the heat treat process.
DG: Justin is not only the lead engineer at DANTE Solutions, he is also the author of an article that just appeared in the March 2020 issue of Heat Treat Today and the title of the article wasProcess Innovation To Reduce Distortion During Gas Quenching. It was a pretty interesting article, something worth reading if you haven't already. It has to do with DANTE controlled gas quench.
JS: I got my bachelors in mechanical engineering degree from Cleveland State. I graduated back in 2015. I actually started interning at DANTE in 2014 and went full-time in 2016. I've been the lead/principal engineer at DANTE with mainly responsibilities of managing projects, training our DANTE users, and offering support to our DANTE users. I helped develop our patent-pending DANTE controlled gas quenching process, which you had just mentioned, and then also a little bit of IT, marketing, sales, and shipping. Being a smaller company, we can kind of do it all.
Fig. 1: Bevel gear axial distortion comparison for an oil quench, high pressure gas quench, and a DANTE Controlled Gas Quench
DG: Tell us briefly about DANTE.
JS: DANTE Solutions is an engineering consulting and software company. We offer consulting services as well as licensing our software. We mainly focus on the aerospace industry, the auto industry quite a bit as well, and we've been starting to get into the mining and energy sectors also. As I said, we are a smaller company. There are six of us right now. Two to three guys mainly focus on the software side, and the rest of us focus on more of the training, the support, and the consulting side of the business.
DG: DANTE is located near Cleveland, OH, and Lynn Ferguson, who has been in the heat treat industry for many, many years, was one of the founders. Let's talk about the genesis of the software. Would you say the software is the core product that DANTE Solutions offers?
JS: Yes, it is. We mainly stay in consulting to stay current and to give those users who don't have the capability to run our software (either they don't have the hardware or they don't have the analysts to be able to do such a thing), so we still offer our consulting services for them. But mainly, software is our main line of business. DANTE was actually formed back in 1982 as Deformation Control Technology, Inc., and we changed our name in 2014 to actually reflect more of the software side, so that's when we changed to DANTE Solutions, Inc.
The project itself that DANTE came out of actually started in 1994 and 1995. It was a collaboration between Ford, GM, Eaton Corp. and then four national labs--I believe they were Los Alamos, Sandia, Oak Ridge, and Lawrence Livermore--and then us as Deformation Control Technology. The whole project came out because those large automakers were claiming millions of dollars of lost scrap from distortion. It was starting to become a major issue and they wanted a way to be able to model the process and be able to optimize the process a little bit better. After that project ended, DANTE somehow ended up with the software, which has worked out well, as we've been able to commercialize it and we've been updating all the material models and the material database for the last 20 years. It's actually come quite a long way.
DG: How did you segue over from auto industry into aerospace?
JS: It just happens that the aerospace components cost a whole lot more than the auto industry components. It was a natural fit once they realized that this software was viable and could do what they needed it to do. And aerospace seems to be more receptive to modeling because their parts are so expensive.
DG: Let's try to put a little flesh on the bones here. For a manufacturer who has their own in-house heat treat for aerospace, automotive, energy or whatever, what makes this software attractive? What makes it viable? Why would someone want it, and why and how do they use it?
JS: Let's start with viability. The first thing is that it is easy to use. DANTE is a set of material routines that link with Abaqus or Ansys finite element solvers. These are solvers that engineers and analysts in the industry already know pretty well, so there is not a lot of learning of new software. DANTE is just a material model, so all you're really responsible for is the material name and what microstructural phases you're starting with. Then we have the ability to modify a few of our control parameters, activating different models; we've introduced stress relaxation, carbon separation, carbide dissolution, and all these different models that you can activate. But the biggest thing that trips people up . . . [is] understanding your process. We like to work with people a lot on trying to help them understand what type of thermal behavior their processes are actually imparting on components. We've done a lot of work with setting up their essentially quench probes and be able to turn around and be able to take that back to heat transfer coefficients that get put into the model. As far as DANTE is concerned, it is fairly easy to use.
We've also developed what they're calling ACT (Ansys Customization Toolkit). It is essentially a series of buttons where you would click on these buttons, fill out information, and then essentially run your models. Abaqus, for the new version of DANTE, we've also developed a plug-in that essentially does the same thing. So DANTE has become very point-and-click. In this world, I think people like that simplicity.
Fig. 2: Axial distortion of a press quenched bevel gear
The next big one would be the accuracy that everybody is concerned about. Our accuracy is due to the models that we use and the algorithms that we employ. There are two types of accuracy. I've touched on the boundary condition accuracy, and that is how your process behaves thermally. That accuracy can be tough to get. It's very doable and we've helped people achieve some really amazing accuracy. The relationship I like to use here is people know static loading models and a lot of engineers have run static loading models. The loads that you put on these static models are going to determine what deflections you get. If your load is not correct, then your deflection will not be correct. In heat treat modeling, the thermal boundary condition is your load. The more accurate your heat transfer coefficient can be, the more accurate your results are. But, with that being said, you can still gain a lot of valuable information from being close enough. We'll talk a little bit about that with the uses and whatnot.
The first important model type that we use is the mechanical model. We use a multiphase internal state variable model. A conventional plasticity model considers stress as a function of strain only, where the internal state variable model actually accounts for the history of deformation by relating the stress to dislocation density. It actually accounts for the history of deformation, which is very important as the steel goes through all the stress reversals that it does going through the process. Our mechanical model defines each phase, so austinite, pearlite, ferrite, bainites martensite, tempered martensite, all of them, as a function of carbon, temperature, strain and strain rate. It also accounts for the trip phenomenon.
For our phase transformation model, we like to use analytical models instead of TTT CCT diagrams, and we do this because you don't get any transformation strain information out of the diagram. So you have no idea how much it is deforming. In order to figure that out, we like to use dilatometry tests to fit to our analytical models. We also account for carbide growth and dissolution during carburizing, which is becoming a major point of interest due to the high alloy content of some of these steels that they're now trying to carburize.
DG: Let's talk a bit more about where manufacturers, who have their own in-house heat treat, might use DANTE's software tool.
JS: One of the big things we like to use it for is what we call sensitivity analysis. This would be, "what happens if my normal process has a little bit of variation?" Or, "what happens if my process parameters change a little bit?" We've also worked into the model now normal material variation. So if your alloy content is a little on the high side, how would the material behave? If it's a little on the low side, how will it behave? [This] is a big deal. One example would be, "I just designed a new part and I want to make sure that it behaves given the range that I know my process can vary." All processes will vary. This is no way to make the process exactly the same every time. Also, in the sensitivity, you can ask the question, “What process variable is a distortion or stress most sensitive to?" By finding out what process variables cause the most sensitivity, then those are the process variables you really need to pay attention to during processing, then the other ones you can just make sure they're in range and leave them alone.
Development and design are two of the big ones that we're trying to get out there that this software can be used for. Everybody knows that it can be used for troubleshooting. Once something goes wrong, yes, sure the software is great and we help figure out a problem; but why not find the problem before it ever even happens? We've been trying to get people to use it for development of new carburizing and nitriding schedules as well as new recipe and design, and even novel processes. You had mentioned our DANTE controlled gas quench. That actually was conceived through all the modeling that we do and watching the response of the material and saying, “Wait a second. If we can control the martensite transformation rate, we can really control the distortion, so let's see if we can do this.” Things like that can come out of the software. Design as well, of optimizing shapes for quench. You can even do quench to fit, which is, "I know my part distorts this much, so let me machine it distorted and then it will fall into shape." Optimizing processes. All of that can be done through design development, and you can find these problems before they ever happen.
Another really big one that I like, and Lynn, our owner, is really keen on this one, is the understanding of your process. When you start to set up these models, you have to ask a lot of questions about your process. What is the HTC of my process, which relates back to agitation in the tanks, part racking, flow directions? You really need to know times and temperatures of every step in your process. So not just the heat to quench, but what about all those transfers in between? All of that needs to be done. So you end up asking a lot of questions like that.
The other one that I always like to say is that the heat treat software removes the black box. In the past, you know what goes in and you know what comes out, but what happens in the middle is kind of a mystery. The software helps you figure out what exactly goes on during your process. It can be very eye-opening.
Fig. 3: Minimum Principal stress of a carburized and oil quenched spur gear
DG: I've talked with James Jan and Andrew Martin over at AVL, and we talked about a variety of ways they use some of their software, and they mentioned that they work with you guys as well, and they were talking about not even just like a quench agitation, flow direction, and things of that sort, but part orientation as it goes into a quench. I assume that would be something also that you guys would be able to help analyze, right? Which way to even put the part into the quench?
JS: Sure, sure. And we've done that. The one that comes to mind is a long landing gear. This landing gear was about 3 meters in length, and we looked at even slight angles going into the quench tank can have serious consequences on the distortion. That is definitely something that we've looked at in the past.
DG: Just that orientation would help, but maybe eliminate vapor stage, or whatever, I assume? Or pockets?
JS: Right. And even beyond that, it sets up thermal gradients in different locations of the part. So now instead of cooling one section faster, you're cooling it a little slower and that kind of thing. That also relates back to actual vapor stages and how bubbles get trapped. But that goes back to defining boundary conditions, which is where software like AVL's FIRE can really be helpful in understanding flow patterns. There is a beneficial relationship there.
DG: There are a host of different materials that people are using. How broad is the database, as far as the different types of materials, that you can analyze and model?
JS: That is a good question. We have a lot of low alloy, medium alloy, and carburizing grades of steel, the 1000 series, the 8600 series, 9300 series, those types of materials. We've also worked with some of the high alloy aerospace grades like C64 and the Pyrowear 53 and that sort of thing. But right now, it's all steel. There is a lot of talk about being able to do aluminum. We get that question a lot.
DG: I was wondering about that specifically- aluminum and/or of course, when we talk aerospace, we're talking titanium. So titanium is not on the table at the moment?
JS: It is, but it isn't. The interesting thing is that there is a phenomena precipitation hardening that goes on in aluminum and titanium. But it also goes on in these high alloy steels. It is a secondary hardening mechanism. We've been working on that and we feel that once we can handle secondary hardening in steel, then the jump to aluminum and titanium should be pretty straightforward.
DG: So to recap, for those of us who are not as well-versed in the product as you are, basically you've got a simulation software that takes into account the material that is being used, also the thermal process (the recipe), which would include both a controlled heat up and potentially a controlled quench. Is that a reasonable way to describe it in a very broad way?
JS: Yes. And also, even the steps before that, like carburizing. If the part is carburized, you would carburize it first. Or nitriding; we've just introduced those models. You can literally do the entire process. And it's not just quenching either. We've done martempering, austempering, normalizing, all of these things. Most all normal thermal processing, DANTE can handle.
DG: The last question I want to ask is, Who is the ideal person/company that would really find the product/service that you're providing useful? I know you mentioned aerospace and automotive, but can we be more specific than that? Where are you finding the most success?
Fig. 4: Displacement versus temperature curves showing the shift in martensite start temperature for 3 carbon levels
JS: That's a tough question. Generally, everybody that has used our software has found real benefit in it. We've tried to get testimonials from a lot of folks, but this can be difficult because of their companies. But from Cummins, we've gotten good responses and also from GM we've gotten good responses. One of them has used it to actually introduce new material and replace legacy material that is now saving them quite a bit of money. GM has used it to look at process design and optimization. But I would say mainly the people that are going to benefit the most are the folks that have an analyst to be able to do the simulation almost on a daily basis. It's one of those things where the more you do, the more you see and the more you understand what is happening. But really anybody that does heat treatment can benefit from understanding what's going on in their process.
DG: You mentioned Cummins, and I'm looking at your website, and I just want to read a paragraph:
DANTE heat treat simulation software has been a great boon to Cummins. Since we've started using their software, we have gone through several projects that have increased our understanding of heat treatment and some of which have saved us production costs. One example was enabling us to gain the leverage needed to make a material and process change on a legacy product that is now saving us at least 25% on material costs. The team at DANTE Solutions has always been very accommodating and is very quick to give assistance and feedback whenever troubles arise, even when the troubles are caused by other parts of the simulation and not DANTE itself. I look forward to working with DANTE team in the coming years as we expand our list of engineers who use this software. -- Brian W. at Cummins
So that leads me to one other question. When a person interacts with you, are they buying software as a service? Is it cloud-based or is it something that they purchase a license for one computer, one user? How does it work?
JS: There are a couple of different ways. They can lease it annually or they can essentially buy the software and lease a license annually. The software can go either on their computer or it can go on a server at their company. We also have options for corporations where you can essentially get software at different locations. We have a lot of options and we can work with customers if they [have] unique needs. That's one of the benefits of being a smaller company, we're pretty flexible like that.
DG: DANTE's mission statement from their website has a nice ring to it: “DANTE Solutions is determined to promote the use of simulation in the heat treat industry. From design to troubleshooting, DANTE Solutions believes everyone can benefit from a little simulation in their life.”
If you'd like to get in touch with Justin Sims at DANTE, please email me, Doug Glenn, directly at doug@heattreattoday.com and I'll put you in touch with Justin.
Doug Glenn, Heat Treat Today publisher and Heat Treat Radio host.
To find other Heat Treat Radio episodes, go to www.heattreattoday.com/radio and look in the list of Heat Treat Radio episodes listed.
It pays to carefully consider the key factors to buying a vacuum furnace (source: TAV, the Vacuum Furnaces Blog)
When and why is it a good idea to purchase a vacuum furnace? Does your company really need one? A company that wants to play its cards best, in terms of investment and yield, knows about the advantages offered by vacuum heat treatments in both the short and long term. But choosing the ideal furnace best suited to your company’s needs isn’t as easy as it might appear.
In this Heat TreatToday Best of the Web feature, TAV Vacuum Furnaces gives readers a handy guide over at its blog to consider the crucial factors in choosing a vacuum furnace for your company, including tips on who needs a vacuum oven, why comparing two or more systems is a bad idea, and the role of the heat exchanger, vessel performance, and the pumping unit.
An excerpt: “There are many fields, ranging from the vacuum sintering of metal powders or ceramics to the vacuum brazing of aluminum alloys to continue with high temperature brazing, in which technological avant-garde stands out. In these sectors, the decision to use a vacuum furnace is linked to the possibility of implementing an advanced development production process, for which the focus was on high-yield plants.”
A global manufacturer of thermal-processing and sterilizing equipment announced they are working with hospitals to prove the efficacy of their Gruenberg product line for dry heat sterilization on PPE and N95 masks for re-use.
Recent tests at a research hospital show positive results in the dry heat sterilization of masks, face shields, gowns and other PPE, with minimal deterioration of the material. During the process, Thermal Product Solutions, LLC (TPS) heated masks to a specified temperature for a calculated period of time that resulted in sterilization of the material. After the sterilization process, fit tests were performed on the masks that passed filtration efficacy, structural integrity, and mask fit. TPS is continuing to work with facilities to further confirm test results.
Greg Jennings, president and CEO, Thermal Product Systems
“We are dedicated to finding methods that aid in protecting the health and safety of all those serving on the front lines during the COVID-19 pandemic,” said president and CEO Greg Jennings. “Our dry heat sterilizers have been used for decades in the decontamination and sterilization of all forms of microbial life and it only made sense to begin testing their efficacy on sterilizing PPE for hospitals and emergency personnel. We are looking to find additional testing partners quickly and ultimately receive FDA approval to help fight the COVID-19 spread.”
Picture 2: Gruenberg Truck- In Sterilizer (source: Thermal Product Solutions)
The Gruenberg sterilizers utilize convection airflow and dry heat for the process. Heat is absorbed by the item being sterilized for a period of time until it reaches the proper temperature needed to destroy microorganisms and achieve sterilization. Dry heat sterilizers range in size from small tabletop models (Picture 1) starting at 1.25 cubic feet (cf) to large truck-in models (Picture 2) offering 1,000cf of sterilization capacity.
Gruenberg’s smaller dry heat sterilizers feature a unique design where the process chamber is sealed throughout the entire cycle, containing any airborne particulates and sterilizing them. Larger chamber systems are easily customized and feature intake and exhaust HEPA filters and several door seal options.
A strong and healthy vacuum furnace system is essential for heat treaters who want to stay competitive and serve their customers well. The heart of the vacuum furnace system is just as critical as the heart of the human body. Just as a healthy heart is essential to living well, keeping a healthy vacuum furnace system pumping strong is essential to certain heat treating operations.
In this Heat Treat TodayTechnical Tuesday Best of the Web feature, Ipsen USA provides tips for how you can get the best performance out of your vacuum furnace by selecting the most appropriate pumping system, and by following a few simple tips for vacuum furnace maintenance over at its blog, Ipsen, The Harold.
An excerpt: “Vacuum furnace systems utilize various types of pumping system combinations to evacuate atmospheric pressure from the vacuum chamber to required ranges for specific processes. Since the heart of the furnace is the vacuum system, it is essential to maintain the pumping system as specified in the operator’s manual, taking into consideration any special accommodations that the type of process being conducted may require.“
This post from Ipsen’s blog guides readers through the basics, troubleshoots common problems, and gives tips for avoiding the heat treater’s primary enemy.
Is new technology always an advantage? Do companies need to update everything or a few things? The rapid pace of technology upgrades is dizzying, and many heat treaters can find themselves unsure of whether to embrace it or refuse it.
In thisHeat Treat Today Original Content feature, Gerry McWeeney of Heat Treatment Solutions gives his take on the pros and cons of remote monitoring in heat treatment.
Special thanks to Gerry McWeeney, heat treatment consultant and president of Heat Treatment Solutions, for permission to run this article.
Technology plays a major role today in most industries, and heat treatment is no different. Having been around emerging technology a lot in the last 20 years or so and reviewing recently other types available in the heat treatment marketplace, it is a subject near and dear to me and I was happy to be sought out by friends in the industry to give my opinion on the Pros & Cons.
THE PROS:
SAFETY – This cannot be reiterated enough. By reducing numbers of labor in operating units, remote capabilities reduce the risk for end-user and vendors.
COST REDUCTION – Reduced labor provides a better commercial proposition to end-users on the manpower to equipment discounted rate scenario.
REMOTE START and STOP
Clients can benefit from early switch on to assist getting weld preheat to temperature. While not ideal for every situation, e.g. inside refineries where conditions can change and the need for the buddy system negates commercial benefit, but, in certain situations can assist welder productivity, which helps cost and schedule.
This reduces the risk in emergency situations. The equipment can be remotely isolated without putting people into the units to do this task.
THE CONS:
REDUCED LABOR - At the site, this can have commercial benefits to the customer. It can also have an adverse effect when scope creep or changes to the schedule occur and there are insufficient resources.
LIMITED FIELD EXPERIENCE - Having control and monitoring operators with limited field experience is a risk as they, at times, can be unable to assist adequately when heat treatment or site conditions change.
RULES & REGS - Differing employment rules and regulations across borders and states can have an adverse effect on project harmony between operators and field personnel.
TOO BUSY – Some operators can be charged with monitoring many heat treatments across various different recording devices and projects, some more complex than others. This can cause delays in communications to field when operators have too much on their hands and conditions change. This can be especially true during TAR / OUTAGE season.
The above lists are not complete--there are other softer pros and cons depending on each company’s technology.
Technology alone will not guarantee the heat treatment, that can only be done by correct set up of thermocouples and heating elements in accordance with code requirements and/or engineered drawings that meet code criteria. Technology is here to stay, and advancements in it, when implemented properly, will help vendors and users alike.
“My preference is for control and monitoring at site using remote capabilities with access to view by the client and heat treatment personnel at site”
Heat resistant alloys used for heat treating fixtures, muffles, retorts, radiant tubes, and other parts are typically stainless steel or nickel based austenitic alloys. Welding of these alloys requires practices that are often exactly the opposite of the practices required for carbon and alloys steels since austenitic stainless steels do not undergo phase transformations. Metallurgists are often asked many questions on the proper welding methods. Carbon and alloy steel welding requires practices and procedures that will minimize or prevent the chances of cracking due to potential martensite formation during weld solidification. Austenitic stainless steels do not undergo any phase transformation. They require rapid cooling to prevent solidification cracks due to hot cracking. Thus different procedures are required.
In this Heat Treat TodayTechnical Tuesday feature, Marc Glasser, Director of Metallurgical Services for Rolled Alloys, provides some basic information on the metallurgy as well as good welding practices to follow.
Reprinted with permission from Heat Treat 2019: Proceedings of the 30th Heat Treating Society Conference and Exposition, October 15-17, 2019, Detroit, Michigan, USA. ASM International, 2019.
CHEMISTRY CONSIDERATIONS
Most heat resistant alloys used in the heat treating industry for components are austenitic. They can be austenitic stainless steels, or austenitic nickel alloys. The key word is austenitic. One of the virtues of austenitic materials is that they are not subject of phase changes from cooling to heating or heating to cooling. This is markedly different from alloy and carbon steels, which undergo a phase transformation from austenite to ferrite and cementite. The cooling must be slow enough to prevent martensite formation, so preheating and postheating are performed to either prevent this phase transformation or to temper any formed martensite.
Austenitic alloys do not undergo phase transformations to martensite, and as a result slow cooling the material is the worst operation that an austenitic alloy can be subject to. In austenitic alloys, the main concern is the tendency for welds to hot tear upon solidification[1]. In stainless steels with up to approximately 15% nickel, the solution is simple. The composition is adjusted to form small amounts of ferrite during solidification[2]. Prediction of the ferrite number FN, which represents an estimate of the amount of ferrite in the weld after solidification, is predicted by using Schaeffler diagrams. The ferrite nullifies the effect of certain trace elements that cause hot cracking [1]. One of these trace elements, phosphorous cannot be refined out of the material. Since these materials are all melted from scrap metal, the amount of phosphorous found in the heat will mirror the amount in the scrap. Sulfur, silicion, and boron also contribute to hot shortness, but these elements can be refined to very low levels in the steelmaking process.
For higher nickel bearing grades, with more than 20% nickel, the chemistry precludes the possibility of ferrite formation. Therefore, other means must be employed to prevent hot tearing during solidification. In this case, the residual trace elements, particularly P must be kept low, as they lead to hot shortness [2, 3]. Certain alloy additions including manganese (Mn), niobium (Nb), molybdenum (Mo), and carbon (C) all reduce the propensity of austenitic nickel alloys and high nickel stainless steels to crack [4]. 310 stainless steel stans in a unique position having neither ferrite formers nor weldability-enhancing alloy additions. In this alloy, control of chemistry and residuals is of utmost importance.
The other key to successful welding of nickel alloys is to minimize the time spent in the high temperature range where they are susceptible to hot tearing [4].
GOOD WELDING PRACTICES
Good welding practices for nickel alloys are centered on the need to remove heat as quickly as possible in order to minimize the time spent in the hot tearing range. The first consideration is to keep the heat input as low as possible to still get a full penetration weld. The actual input in kJ is dependent on the alloy being welded.
Heat input (HI) is defined as: HI (KJ/in) = Voltage x Amperage x 6/(Speed (inch/min) x 100)
Welds should NOT be preheated and interpass temperatures should be 200°F maximum. The cooler the interpass temperature is, the less likely hot tearing is [5]. A reliable, easy test for a welder is the spit test. Spit on the weld, and if it boils it is still to hot, and further waiting is in order.
One of the most important considerations in welding nickel alloys is to weld in a straight line along the length of the weld and do not weave. Welders tend to weave from side to side especially when welding nickel alloys which are more viscous that carbon steels and this weaving makes the metal flow better. While this technique works well for carbon steel where a higher heat input and slower cooling are necessary, it is exactly the wrong procedure for nickel alloys. Weaving tends to flatten out a weld. This in turn reduces the crown height and strength.
Furthermore, weaving tends to increase the heat going into the weld and slow down the weld speed. The key is to get a nicely shaped, convex weld bead, as illustrated in Figure 1. A concave bead configuration tends to crack along the centerline [5].
Figure 1: Convex vs. Concave Weld
Full penetration welds are important. Beveling one or more of the pieces to be joined may be required to get a full penetration weld. Incomplete penetration leaves a void between the two workpieces. Such a channel can entrap surface treating gases leading to brittle pieces surrounding the weld. Furthermore, the gap can act as a propagation site for cracks which form from thermal cycling from heat treating. This is shown in Figure 2 below.
Figure 2: The effect of non fully penetrated welds
Some suggested joint designs include square butt joint, single V joint, double V joint, single U joint, double U joint, J groove joint, and T Joint. These are shown in Figures 3 to 9 below, along with design criteria. These suggestion grooves are from ASME code[6], but are good guidelines to follow even if code stamps are not required.
Figure 3: Square butt joint. Maximum t = 1/8 ” Gap A = 1/16″ Minimum, 3/32″ Maximum
Figure 4: Single V Joint. Maximum t = 1/2″ Gap A = 1/16″ Minimum, 1/8″ Maximum Land B = 1/16 to 3/32″ Angle C = 60 – 75 degrees
Figure 5: Double V Joint. Gap A = 1/16″ Minimum, 1/8″ Maximum Land B = 1/16 to 3/32″ t = 1/2″ or greater Angle C = 60-75 degrees
Figure 6: Single U Joint. Gap A = 1/16″ Minimum, 1/8″ Maximum Land B – 1/16 to 3/32″ Radius R – 3/8″ Minimum For single groove welds on heavy plate thicker than 3/4 inch. Reduces the amount of time and filler metal required to complete the weld.
Figure 7: Double U Joint. Gap A = 1/16 to 1/8″ Land B = 1/16 to 3/32″ Radius R = 3/8″ Minimum Minimum t = 3/4″
Figure 8: J Groove Joint. Gap A = 1/16 to 1/8″ Land B = 1/16 to 3/32″ Radius R – 3/8″ Minimum For single groove welds on plates thicker than 3/4 inch. Reduces the amount of time and filler metal required to complete the weld.
Figure 9: T Joint. t = greater than 1/4″ For joints requiring maximum penetration. Full penetration welds give maximum strength and avoid potential crevices.
Regardless of which joint is selected, the purpose is to obtain a full penetration weld with no voids or channels, as shown in Figure 10 below.
Figure 10: Example of Full Penetration Weld
Both the starting and finishing ends of the weld beads can be crack initiation sites. The best practice for starting is to make the start of the weld bead as heavy as the rest of the weld bead [4]. A light or thin start up can cause cracking. This is shown in Figure 11. Furthermore, in nickel alloys, the end of the bead can sometimes yield a star shaped crack. This can be eliminated by backstepping the weld for ½ to 1 inch as shown in Figure 12 [3].
Figure 11: Start welds as heavy as the rest of weld beads
Figure 12: Backstep the weld ends to prevent cracking
Cleanliness is extremely important for welding stainless and nickel alloys. Some general rules include [5]:
Remove all shop dirt, oil, grease, cutting fluids, lubricants, etc. from welding surface and on the area 2 inches wide on each side of the weld joint with suitable cleaning agent.
Eliminate all sources of low melting metal contaminants from paints, markers, dies, back up bars, etc. Chromium plate copper back up bars can form a barrier between copper and the weld surface. Copper can cause HAZ cracking in nickel alloys. These low melting contaminants cause cracking and failures in nickel alloy and stainless steel welds. Avoid using lead or copper hammers in fabrication shops.
Grind clean the surfaces and the HAZ areas. Chromium scales melt at higher temperatures than the base metals and will not be reduced by filler metals.
When welding to nickel alloy or stainless to plain carbon steel, the plain carbon steel must be ground on both sides too.
SHIELDING GASES
Bare wire welding requires a shielding gas to protect the weld from oxidation, loss of some elements to slag or oxide formation, and contamination.
Most stainless steel and nickel alloys require 100% argon for shielding for the GTAW or TIG process.
GMAW or MIG welding has two distinct modes of metal transfer. Spray arc processing transfers metal between wire tip and workpiece as droplets. Short circuit processing transfers the metal in sheets or globules. The most common shielding gas for spray arc GMAW welding is 100% argon. 10-20% helium can be added along with small amounts of carbon dioxide (1% max) to improve bead contour and reduce arc wander [1]. Short circuit GMAW welding uses blends of inert gases usually either 75% argon – 25% helium or 90% helium – 7.5% argon – 2.5% carbon dioxide.
In order to prevent hot cracking with the GMAW process, 602CA® requires a unique blend of 90% argon – 5% helium – 5% nitrogen and a trace (0.05%) carbon dioxide. This blend was trademarked as Linde CRONIGON® Ni30. It is not readily available but there are other close alternate quad gas blends that are commercially available. For GTAW welding, argon with 2.5% nitrogen is used to prevent cracking in 602CA. The nitrogen is the key to preventing cracking in 602CA regardless of method.
RESTRAINT AND DISTORTION CONTROL
Weld metal shrinks as it freezes. To accommodate the dimensional changes associated with freezing, either the base metal or the weld must move to prevent cracking or tearing. In complex assemblies with multiple welds, each weld, when solidified functions as a stiffener, further restricting movement of subsequent welds. In such cases, the most difficult or crack susceptible weld in the assembly should be made first and the easiest and strongest welds should be made last [5]. An example is shown in Figure 13 below.
Figure 13: Welding with multiple welds. In this example, the edge weld on the left would be the first weld made. The fillet weld in the middle should be the second made, and the butt weld on the right would be the last one made
When multiple tack welds must be made, they should be sequenced along the length of the plate [5]. Tack welding from one end to the other that is made in order will result in plate edges closing up as shown in Figure 14.
Figure 14: Tack welding in order along plate edge (left) can close up and distort the joint. Sequencing the tack welds (right) can greatly reduce distortion
Finally, multipass welds should be sequenced around the center of gravity of the joint as shown in Figure 15 below.
Figure 15: Proper sequencing of multipass welds
REFERENCES
[1] Schaefer, Anton L, Constitution Diagram for Stainless Steel Weld Metal. Metal Progress. ASM, Metals Park, OH. P 680-683. November 1949.
[2] Ogawa T. & Tsunutomi, E. Hot Cracking Susceptibility of Austenitic Stainless Steel. Welding Journal, Welding Research Supplement. P 825-935. March, 1982
[3] Li, L & Messler, R. W. The Effects of Phosphorous and Sulfur on Susceptibility to Weld Hot Cracking in Austenitic Stainless Steels. Welding Journal. Dec. 1999, Vol 78, No. 12.
[4] Kelly J. Heat Resistant Alloys. Art Bookbindery. Winnepeg, Manitoba, Canada. 2013
[5] Kelly J. RA330, Heat Resistant Alloy Fabrication. Rolled Alloys. Temperance, MI. May, 1999
[6] ASME Boiler and Pressure Vessel Code. American Society of Mechanical Engineers. New York, NY. 2013.
A machine tool manufacturer has decided to create their own “captive” heat treat department. The company has consequently invested in two different, yet complementary, vacuum heat treatment furnaces.
The CaseMaster Evolution® multi-chamber vacuum furnace (source: SECO/WARWICK)
As is often the case with companies thinking about how to gain better control of their production systems, one of the obvious bottlenecks for the customer was their offsite heat treatment arrangement. While quality from their existing suppliers was not an issue, it was clear that logistics could certainly be streamlined by eliminating the need to outsource parts to an external heat treater. The furnace manufacturer helped them weigh the pros and cons of moving their heat treatment processes into the plant. Ultimately, a decision was made to set up their own department, invest in new vacuum heat treat equipment, and train their production technicians to perform this critical function of the plant.
SECO/WARWICK received an order for a multi-chamber carburizing vacuum furnace with integral gas or oil quench, and a high pressure gas quench vacuum furnace capable of quench pressures up to 15-Bar.
The Vector® 15-Bar high pressure gas quench vacuum furnace (source: SECO/WARWICK)
“We knew the customer was already getting excellent quality from their supplier, so the question was ‘How can we make the process better?’” said Maciej Korecki, VP of Business Segment Vacuum Heat Treatment Furnaces at SECO/WARWICK. “Starting an in-house heat treat department requires some amount of risk tolerance by ownership, and they needed assurance that the return on production improvements would be worth the investment. [We have] the background to help make those determinations, and as a manufacturer of heat treat equipment, the company was able to offer real-world experience on performance that an independent consultant might not be able to provide.”
Welcome to the inaugural column of Heat Treat Today‘s first offering of This Week in Heat TreatSocial Media. As you know, there is so much content available on the web that it’s next to impossible to sift through all of the articles and posts that flood our inboxes and notifications on a daily basis. So, Heat Treat Todayis here to bring you the latest in compelling, inspiring, and entertaining heat treat news from the different social media venues that you’ve just got to see and read!
1. Entropic Time (Backwards Billy Joel Parody) by A Capella Science
Let’s start your Friday off with this energetic, fun, and educational video that Paul Mason of Thermo-Calc Software shared. (And, you’ll be singing the song all day! You’re welcome!)
2. COVID-19
We have all been affected by the COVID-19 virus. It has produced experiences that none of us has ever ventured through before in our lifetime.
Additionally, many of the heat treat companies have shared their statuses and plans for business via social media posts. Here are a few of them:
3. What’s So Cool About Manufacturing?
Check out Abbott Furnace Company’s collaboration with Saint Mary’s Area Middle School to introduce kids to the world of manufacturing.
4. Reading and Podcast Corner
You may have a bit more time to catch up on the reading and podcast listening you’ve been yearning to do. May we recommend two brief articles written by industry experts and an informative podcast.
Check out Gerry McWeeney’s article, “Pros and Cons of Remote Monitoring in Heat Treat”
For those of you interested in medical devices.
And, for your listening pleasure, be sure to download the latest Heat Treat Radio episode entitled, Women in Heat Treat, with Ellen Conway Merrill and Rosanne Brunello. They will inspire you!
5. Launch into Your Weekend with a Reading by Jackson
No additional caption needed! Happy Friday, everyone!
(Editor’s Note: Users of Firefox may have difficulty playing the below video. If so, please use another browser like Chrome.)
