You may hear the term “White Iron” and wonder why Lawton’s steel foundry makes it?
Well, white iron came about in the 1900s, when researchers discovered that adding nickel and chromium to iron can really improve the hardness.
The very interesting part here is that white iron is super hard, but at the same time very fragile and prone to cracking in the casting process.
We sat down with Lawton Novi Industrial Engineer Nick Knotts to discuss the ins and outs of white iron and why it may be the perfect solution for your abrasive needs.
The History and Applications of White Iron
In the early 1900s, someone discovered that if you added nickel and chromium to cast gray iron you can create super high hardness and tons of carbides.
“It’s basically cast iron without graphite,” said Knotts. “In a lot of cases it carries a lot of chrome and nickel.”
Knotts continued to talk about the wide variety of grades and sub-sections of white iron. “So pretty much the main seven are covered in ASTM-A532, which covers the Ni-Hard alloys.”
Ni-Hard was trademarked for a long time, but that trademark has expired as the ASTM is now using it.
It gets it’s name from the nickel (and chromium) added to it and it’s super hardness… hence “Ni-Hard.”
“The most common subset you hear of,” said Knotts, “pretty much covers everything from 4% all the way up to 25% chromium.”
White iron is used to be wear-resistant against abrasive materials like minerals, gravel, limestone, etc.
“So typically the people who should be using white iron are those who have abrasion-resistant applications that don’t involve a lot of impact,” said Knotts. “White iron also doesn’t do well in metal-on-metal wear.”
So now, we all understand that white iron is known for it’s hardness, but there is way more to it according to Knotts. “The hardness is actually just a symptom or side effect of the actual cause,” said Nick. “The real reason it’s so abrasion-resistant is because of the carbides in the microstructure.”
Those carbides basically make it really difficult for a very fine particle that’s very hard to carve a gouge all the way through the microstructure of white iron.
The base matrix is usually martensite (if you quenched and tempered it) or austenite. The carbides are much harder than both, often times over 1,000 Vickers hardness.
“So either the minerals or materials have to break that carbide, which is not easy,” said Knotts, “or it has to chip it out and remove it over time, which also isn’t easy.”
So primarily what white iron does is buys you time before you can wear out significant portions of the microstructure, slowing down the general rate of wear.
The Interesting Dilemma: High Hardness, but also Super Fragile
Despite being super hard and abrasion-resistant, white iron lacks toughness.
“Those carbides, because they have such a high hardness on a micro scale, they have no ductility,” said Knotts. “it’s really easy to brittle fracture them, but at the same time it’s really hard to get hard minerals or materials through it.”
Knotts says the pouring process for white iron is fairly simple, even easier than some gray or ductile iron where you have to add magnesium treatments or inoculation or both. “When it comes to shakeout is where it gets hairy. Pretty much anything you do that induces impact, like throwing it in a bin, you can crack the part and ruin your day.”
He says he has seen plenty of white iron crack after it was poured. From white iron castings falling off a grinding table to forklifts picking up and dropping the castings after shakeout, there are many ways white iron can crack.
“I’ve also seen many times when someone tries to install a white iron casting,” said Knotts. “These white iron wear liners have bolt holes and I’ve seen it so many times where they don’t use a torque wrench or use it improperly, or they tighten one bolt down right away before tightening the others, leading to it breaking right in half.”
Knotts says the main reason it lacks true tensile strength is when you pull it in tension, it doesn’t have a lot to hold together. White iron also doesn’t do well in compression and it does terrible against uneven loading.
“It essentially has no impact toughness,” said Knotts. “I think some people have actually hit Charpy bars out of white iron and the toughness was basically non-existent.” “The other thing I would add is it’s very sensitive to heat too.” You can somewhat improve white iron’s hardness through quenching and tempering. “When you quench and temper white iron it typically turns the austenite into martensite,” said Knotts. “What that does is make the general matrix harder as opposed to when it is just austenite.”
On top of all of that, you basically can’t weld white iron because of how high the hardness is. “You’d have to preheat the castings to temperatures that are ungodly,” said Knotts. He added that heat treatment can be very tricky too, having to be careful you don’t ramp up or down too quickly.
Choose Lawton Novi When it Comes to Your White Iron Needs
Yes, white iron can be fragile, but it’s also a great material in its right application.
“You can say white iron is a terrible material if you were talking about a structural load bearing component, you’d be right. But if you’re talking about an abrasion-resistant component, you couldn’t be more wrong,” relayed Knotts.
The dominant thing Lawton Novi produces are wear liners, most commonly used for cement applications. Knotts said Novi also has made idler wheel rails, idler wheel shoes and slurry nozzles out of white iron. Those are predominantly made from class 1A white iron, but Novi does pour all of the Ni-Hard grades, as well as all others beyond Ni-Hard upon request.
“The one stipulation we probably make with white iron is anything over 6 inches of section thickness,” said Knotts. “It becomes really difficult at that size to prevent the part from cracking during solidification and/or heat treatment.”
Knotts said white iron can be used in pretty much any application in which you see a lot of abrasive wear from materials that are not metal. Those include minerals, limestone, smaller rock chunks, gravel and sand.
The biggest advantage of choosing Lawton Novi is the ability to offer you custom solutions.
“Just recently we worked with a new customer on a solution for a particularly troublesome application,” said Knotts. “They were using white iron for it, but they probably weren’t using the right grade and weren’t performing the heat treat properly. We looked at it, addressed it and offered them a tailored solution to their problem.”
Knotts said Novi also has dealt with people looking to make their steel plates more wear resistant. Since they were using it in a mineral abrasive situation, Novi pushed the company towards a white iron solution.
“The other thing is we can tailor those solutions on a cost-basis,” said Knotts. “A lot of times the white iron wear part isn’t the first part to wear out in those systems, so we can take offer lower costs on them by avoiding expensive quenching and heat treatment.”
If it is a really abrasive application, Lawton Novi has no problem offering quench and heat treat or even a higher alloy material.
“One big thing people don’t talk about is that Lawton Novi has the ability to make pretty small run batches of white iron, cost effectively,” said Knotts. “Lawton Novi has the flexibility to make those small batches.”
We can all agree white iron is best used as an abrasive wear part for minerals and materials that are not metal. “That being said,” Knotts butted in, “if you have an application that involves high impact or involves metal-on-metal, call us.” “We can help you with that too as we have solutions for metal-on-metal wear, we can make steels that do well in metal-on-metal wear and it if it has high impact we can make you austenitic manganese steel.”
More About What Lawton Novi Can Provide for You
Lawton Novi is a specialized steel casting foundry making steel, stainless steel, white iron, superalloys, low alloy steels and much more.
Our castings and machined components are known for being heat-resistant, corrosion-resistant and abrasion-resistant.
We can handle castings from 2 pounds all the way up to 5,500 pounds with our no-bake sand molds.
Check out Lawton Novi’s capabilities here.
More on Industrial Engineer Nick Knotts
Lawton Novi Industrial Engineer Nick Knotts recently was named IACMI-The Composite Institutes Rising Star in Manufacturing. He was one of five winners of the inaugural award.
Nick is a member of the Steel Founders Society of America and is the chair of the Future Leaders committee, as well as a member of SFSA’s Technical and Operating Committee. He has won back-to-back SFSA Founders’ Choice Awards for his research on mold wash systems, including work to reduce gas and inclusion issues in steel castings
Knotts was also a judge for this year’s Cast in Steel competition in Grand Rapids, Michigan. He has also helped mentor teams from Michigan Tech in the past two years of Cast in Steel competitions.
You can also read Nick’s “Man of Steel” blog series online here.