Precision Machining Essentials: Material Types and their Differences

Precision machining helps to create accurate and specialized parts for some applications. Because of the diversity of parts needed, precision machining providers need to be able to work with a variety of different materials while maintaining the same quality, precision, and accuracy. Precision machining is efficient for polymers, plastics and various metals and alloys including aluminum, stainless steel, copper, tellurium copper alloy, titanium, Tungsten, Kovar, Ni 200, Inconel, and Nitronic 60. Here we take a closer look at a few of the most common material types and the differences between them that can affect machining and performance.

STAINLESS STEEL

Stainless steel is a popular material for use in precision machining as it is versatile, durable and efficient. However, there are a number of options and varieties to choose from when it comes to stainless steel. Different types of stainless steel can be used for various applications in precision machining to achieve the desired result.

Stainless steel is an iron-based alloy that contains at least 10.5% chromium. Chromium is the component that allows stainless steel to be ‘stainless’ and resist corrosion. One of the ways to categorize stainless steel types is according to the metallurgical structure. The three main varieties of stainless steel categorized by crystal are austenitic, ferritic and martensitic, the heat treatment changes crystal structure and alloying changes the grade of the stainless steel.

steel sheet in precision machiningAUSTENITIC STAINLESS STEEL

Austenitic stainless steel is alloyed with chromium and nickel as well as manganese, molybdenum or nitrogen. Austenitic stainless steels are known for their exceptional corrosion resistance, the ability to be formed efficiently and effectively, and good yield strength, tensile strength and high impact strength, these are the 300-series grades and can only be hardened by cold-working.

Austenitic stainless steels (that are not free-machining) are considered to be tough to machine. However, their properties can make them ideal for the final part or component.

NON-AUSTENITIC STAINLESS STEELS (FERRITIC AND MARTENSITIC)

Non-austenitic stainless steels are both straight chromium alloys, with martensitic steels having a higher carbon to chromium ratio than the ferritic stainless steels. Non-austenitic stainless steels are the 400-series grades. They are magnetic and have a lower corrosion resistance than their austenitic counterparts. However, non-austenitic stainless steels are hardenable by heat treating and are less expensive.

FERROUS VS. NON-FERROUS METALS

Another way to categorize metals used in precision machining is by iron content. Metals that contain mostly iron are called ‘ferrous,’ while metals that contain no iron are called non-ferrous. Ferrous metals include stainless steel and cast iron. Aluminum, copper, tellurium copper alloy and titanium are non-ferrous metals.

In general, ferrous metals are magnetic and are less resistant to corrosion, but as mentioned above different alloys can alter these properties, making ferrous metals more corrosion resistant or even non-magnetic.

METAL ALLOYS AND THEIR USES

In basic terms, a metal alloy is a mixture of two or more metals, or a metal and another element. Metal alloys have different properties than the metals or elements on their own, which changes their functionality for precision machining. Alloys can provide the benefits of individual metals while counteracting their drawbacks. For example, stainless steel is an alloy of iron, carbon, chromium and other elements in it’s purest form. The iron provides strength, durability, and magnetism, while the chromium helps to provide corrosion resistance by adding vast amounts of nickel and/or chrome and molybdenum. These are the class of Superalloys. Alloys offer higher performance and versatility and have a range of uses in precision machining.

Choosing the right material type for your project relies on a number of factors including budget, quality and performance requirements. Talk to a professional precision engineering provider today about what materials would best suit your project.