The great diversity of hand tools that we all use, whether at home, in the workshop, industry or in the various trades and professions, provide us with unsurpassed utility. Let us think, for example, of how essential a combination wrench, a parrot beak pliers or a pliers of any type is for a variety of tasks that our hand is unable to perform.
For the most part, these noble tools are built in Carbon Steel, an extremely resistant material that guarantees a long useful life. Through special treatments or coatings of the steel, a special range of tools for specific purposes has also been achieved, as is the case of isolated tools.
However, there are work environments where the use of manual tools Carbon steel is not recommended, or it may develop problems over time. Precisely these problems arise when carbon steel begins to present its disadvantages, which are, 1) contamination in other materials and 2) tendency to rust in corrosive environments.
These disadvantages are unacceptable when these tools They are used in industries, for example, automotive, naval, construction, aeronautics, chemical, energy, electronics, oil, nuclear, etc. Nor can contamination and oxidation be allowed in the pharmaceutical, food, biotechnological or medicinal industry, or in demanding environments such as clean rooms, laboratories, water treatment plants and wet or underwater places, for example.
In these environments, the use of a conventionally manufactured screwdriver or hammer can wreck complex steps that ensure sterility and environmental integrity in sensitive manufacturing operations. Therefore, the use of manual tools suitable for installing and maintaining processing line machinery in particular environments is an essential element of current good manufacturing practice in critical areas.
It is in the face of these demands that technology has recently advanced with the design of the same hand toolss that we know, but built with a material that is by no means unknown to us, but that is capable of coping with these difficult environments: the stainless steel.
So before we go any further, let’s start with the obvious question. What is stainless steel?
What is stainless steel?
In the early 20th century, metallurgists noted that chromium had a greater attraction to oxygen than iron, so they added a low amount of chromium to steel. Studies have shown that when at least 10% chromium is added, it binds with oxygen to form a highly resistant transparent layer on the surface of the steel, which prevents rust by eliminating the possibility of oxidation.
Therefore, the stainless steel It is a low carbon alloy containing at least 10% chromium to resist corrosion. Contact with oxygen forms a passive (ie, non-reactive) surface film of chromium oxide that does not contain iron, unlike ferrous chrome-plated surfaces. Furthermore, when the passive film is damaged by scratches, wear or dents, the oxygen in the air can regenerate it.
The stainless steel it is a material of enduring beauty, as it also resists the corrosive attack of many acids. It possesses strength and toughness at both ends of the temperature scale, yet can be manufactured into intricate shapes for many uses. Due to this exceptional versatility, the stainless steel warrants careful consideration for any product that requires one or more of the following properties:
- corrosion resistance
- Resistance to elevated temperatures
- Strength and ductility at cryogenic temperatures
- Oxidation resistance at elevated temperatures
- Abrasion resistance
- Good looks
There are more than 250 different stainless steels that are divided, according to their crystalline structure, into five large families or classes, developed to consolidate the chemical and mechanical properties required by specific customer applications. So we have classes steels that are more resistant to corrosion, others that are more resistant to traction and others that are harder.
One of these families is the one that makes up the martensitic stainless steels. These are extremely strong and resistant, as well as highly machinable, magnetic and tempered materials that can be hardened by heat treatment.
In turn, the American Iron and Steel Institute (AISI) created various degrees of stainless steels widely accepted globally. These grades are identified by numbers, from the 100 to the 600 series, where each is organized by alloy and grain structure. The most used in manual tools is the 400 series, which covers both ferritic and martensitic structures, although the latter are preferred for tools. The steels of 400 series They contain between 11.5% and 18% chromium, as well as higher levels of carbon than ferritics, and are widely used in the manufacture of surgical and dental instruments, cutlery, scissors, valves, bearings, sporting knives, and various tools. Of the various 400 series steels, the 420 stainless steel is the star of hand tools.
Characteristics of 420 steel
The AISI 420 stainless steel it is the one chosen by many manufacturers, since it optimally combines the different properties required for the manufacture and use of tools of stainless steel. In the following table we detail some of its properties.
Why use 420 steel tools and not carbon steel?
The integrity of critical machinery that complies with current regulations can be compromised by routine cleaning or maintenance operations with manual tools incompatible.
For example, a sterilized screwdriver Carbon Steel It is still an iron tool that should never come into contact with non-ferrous materials such as stainless steel, as free iron will naturally migrate to the carbon steel surface. Autoclaving tools between uses is believed by many to provide protection for working in a sterile environment. However, while this is initially effective, each successive sterilization cycle degrades the coating that is applied to carbon steel (or chrome vanadium steel) for corrosion resistance.
After about 20 autoclave cycles, that coating can deteriorate, flake and peel, creating a second source of particles that compromise any process that requires a sterile environment. Chromium particles from carbon tools that are repeatedly autoclaved contaminate sterile processes, either directly from the tool or from the hands or safety clothing of the operator. This potential for contamination is especially problematic for food processing, hospitals, biotech labs, scientific research, microchip production, or other high-tech products.
In short, the sterilization is not enough to ensure the effective operation and long-term integrity of the manual tools. Instead, the solution is provided by the stainless steel tools that have become the standard for industrial processes with risk monitoring.
Summary of utilities
Today we will find in the market a wide variety of stainless steel tools, provided with resistance, hardness and torque capacity of industrial grade, which we can purchase individually or in multi-piece kits offered by some manufacturers. In addition to those already mentioned in this article, we can add, among others, wrenches, socket wrenches, Allen and Torx keys, cutters, punches, pressure pliers, spatulas, chisels, torque wrenches, vices, scissors and even portable modules to store these tools.
Our needs and work environment will determine the type of manual tool that we want to use or acquire, so in the following table we present a comparison between the main characteristics offered by conventional tools of Carbon Steel and the tools of stainless steel when it comes to applying them in environments that require special care and precautions such as those mentioned above.