The impact of stainless steel tools or stainless steel tools in environments where the use of their carbon steel peers can cause inconveniences, has continued to expand over the last 15 years. Its benefits are considerable and many companies in various industries assume the cost 10 times higher than the stainless steel tools over those of carbon steel with the full assurance that the sterility, hygiene and/or environmental integrity of its processes will remain intact, at the same time as the durability of its manual tools will multiply remarkably.
Given their peculiarities and the special niche they cover, it is unlikely that the hobbyist or trade worker will opt for the use of a stainless steel tool. However, the demand for this type of article from industries such as food and beverage, pharmaceutical, biotechnological, aeronautical and nuclear, among others, is increasingly growing. Another important market is the construction industry, since numerous stainless steel tools, such as, among others, trowels, spatulas, hammers, wedges or hacksaws, are not only more resistant and durable than those made of carbon steel, but also have an elasticity and flexibility that facilitate use for longer periods, reducing fatigue of the user. employee.
In this note, therefore, we are going to point out some characteristics of the stainless steel tools that should be known not only by those who acquire them, but also by those who use them.
a) Magnetic and non-magnetic tools
While there are thousands of possible alloys of stainless steel, only about twenty are in common use. The ability or otherwise of a steel to be hardened by heat treatment groups these alloys into four main categories, each exhibiting a different level of magnetic characteristics:
- Austenitic steels (300 series)
- Martensitic steels (400 series)
- Precipitation hardening steels (17-4PH, 455 series)
- Ferritic steels (430 and 443 series)
All austenitic stainless steels (304, 316, and 316L series) are nonmagnetic in the fully austenitic state, as is the case in well-tempered alloys. The other alloys are magnetic to varying degrees.
Some manufacturers select one, more than one, or all of these alloys to make their tools, and that selection is based on the physical characteristics required for proper tool performance.
In general, most manufacturers mainly have their range of tools magnetic stainless steel, that is, made with alloys 420, 440, 17-4PH, 455 and 465. Martensitic steels 420, 430 and 440 have lower corrosion resistance than steels 17-4PH, 455 and 465, and are very little resistance to alcohol/hydrogen peroxide mixtures.
All alloys are turned into the ultimate tool by machining, casting, or forging, and are heat treated, polished, and passivated before being placed on the market. The passivation is the operation performed to remove free iron from the surface of stainless steel. There are several passivation processes, including a novel one using citric acid that is more environmentally friendly than traditional methods using nitric acid. The removal of free iron facilitates the interaction of the chromium contained in the steel with oxygen, resulting in the formation of a passive (ie non-reactive) oxide layer. This thin, invisible layer protects the material against corrosion thanks to its ability to self-repair: if the metal is scratched and the passive film deteriorates, more rust will form and cover the exposed surface. If the scratches are deep, the tool can be passivated again.
In the last decade some manufacturers have developed a complementary range of manual tools stainless steel non magnetic, based on BioDur® 108 alloy steels and the austenitic 300 series. These non-magnetic tools are designed to meet the demands of industries such as avionics, aerospace, electronics, MRI devices or silicon wafer factories, where it is essential the absolute absence of magnetic permeability, residual magnetism and electrostatic discharges. Both alloys are highly resistant to corrosion and BioDur® 108 is of “implant quality” for use in medicine.
From this it follows that, depending on the application and its requirements, the choice of a magnetic or non-magnetic stainless steel tool is very important, since each type has its specific use. Knowing this classification of stainless steel tools it will guide us in our selection and avoid purchasing an alloy that is not suitable for our specific purpose.
b) More resistant and less resistant steels
Although one of the main properties of stainless steel is its great resistance to corrosion, abrasion and oxidation, both at low and high temperatures, we should not interpret that all steels can equally withstand any type of chemical or gaseous process. .
This means, for example, that if our company is going to implement or validate a cleaning program for stainless steel tools, not only the type of alloy to choose, but also the chemical composition of the cleaning solution must be considered in advance.
For example, as noted above, Alloys 420, 430, and 440 (martensitic steels) have very poor resistance to mixtures of alcohol (eg, ethanol or isopropyl alcohol) and hydrogen peroxide. If the cleaning system employs these highly corrosive solutions, it is preferable to use tools made from other alloys, such as 316, 17-4PH or 455, which have better strength but are more expensive than martensitic steels.
Also keep in mind that all stainless steels require oxygen to keep the passive chromium oxide layer intact. If the tool is used in an oxygen deprived environment, it can rapidly corrode in various ways and cause serious inconvenience. An example of this case is underwater applications, where a special selection of the alloy is required, as well as different previous tests and special maintenance of the tool.
c) Some particular characteristics of the tools
As with their carbon steel lines, fabricators design many of their manual tools stainless steel with certain characteristics that give better grip, or greater capacity or quality of cut. Therefore, it is convenient that when choosing a tool we look at some technology details that may be useful for our application.
I) Type of tip of the screwdrivers: while most manufacturers offer their stainless steel screwdrivers with a conventional Phillips tip, others incorporate a tip provided with slots subjected to laser treatment, which forms sharp edges that allow a perfect fit between the screwdriver and the screw head, preventing the screwdriver from loosen during use and cause damage to the user and/or the surface.
II) Type of construction of the pliers: We should always inspect the build quality of these tools as well as the sharpness of the edges. Some brands present their line of pliers with an excellent articulation system between the two halves of the tool, made up of a finely threaded screw and nut mounted on very precisely machined bearing rings, which ensures perfect and firm alignment. as well as an even and consistent cut. Other brands market pliers subjected to a dual sharpening process and endowed with great resistance and hardness through an induction heating and tempering process. This offers very sharp, hard and resistant cutting edges. While some manufacturers have pliers with edges of flush cut, others also offer their line of pliers with edges of almost flush cut, each of which will serve different purposes.
III) Stainless Tool Kits: If we work with the same tool that requires different types and/or sizes, we can opt for practical kits or sets offered by some manufacturers. Among others, there are socket wrench kits, screwdrivers, drill bits and Allen keys, pliers, tweezers, etc., as well as kits of various tools for a specific professional or craft purpose, for example, bonsai kits, kits for uses in dentistry, medicine, biology and other scientific branches.
d) Care of stainless steel tools
There are two fundamental aspects to take into account with stainless tools: one is related to use/maintenance and the other to sterilization.
When we use or store a stainless tool we must take care that it does not make contact with a carbon steel one. Contact-prone situations are, for example, using stainless wrenches on carbon steel screws or storing stainless tools in carbon steel tool boxes, either with or without other carbon steel items. This causes a gradual deterioration of the steel due to the transfer of carbon steel particles to the stainless tools.
If this is our situation, we can passivate the stainless tools contaminated in a citric or nitric acid bath (as above) to remove surface iron and restore the normal passive layer.
We should also be aware that any stainless steel alloy will discolor and corrode if exposed to high concentrations of the following chemicals: sodium hypochlorite (bleach), scale and stain remover, aluminum chloride, barium chloride, bichloride mercury, calcium chloride, carbonic acid, iodine, chlorinated lime, ferrous chloride, Lysol, mercury salts, phenol, tin chloride and hydrochloric acid.
During the sterilization process, it is essential to follow a series of practical tips that will prevent pitting, staining and discoloration, and ultimately extend the life of the product. Let’s review the main ones.
- Separate stainless steel tools from carbon steel, anodized aluminum, titanium nitride and all types of carbide. This means that tools of different compositions must be treated separately throughout the sterilization process. This will prevent cross corrosion of stainless tools.
- Thoroughly wash and completely dry the tools before placing them in the sterilization bag.
Special care of articulated tools
- All articulated tools (pliers, scissors, pliers, tweezers) must be thoroughly cleaned before sterilization.
- Dry completely in the open position to remove water and chemicals.
- Do not allow hinged tools to be exposed to water or moisture. This can cause discoloration, staining, and affect performance.
- Lubricating oils and sprays prevent rust, corrosion and joint stiffness. Routine lubrication ensures smooth and continuous operation.
- Autoclaving is the preferred method of sterilization; Only use autoclaves that have temperature, pressure and operating cycle controls.
- Steam sterilizers and vertical autoclaves are not recommended because the temperature cannot be kept constant.