UGIMA® 4598 Solution Annealed

Cold drawing – Roll forming

UGIMA® 4598 is suitable for cold forming by conventional methods.

Cold deformation increases the mechanical properties (Rm and Rp0.2) of the grade and reduces its ductility. A solution-annealing heat treatment at between 1020°C and 1120°C can be used to reduce the hardness of UGIMA® 4598 and restore its ductility.

UGIMA® 4598 is less work-hardened than type 1.4404 grades as it exhibits greater stability with respect to strain-induced martensite formation. Thus, for a total section reduction of 95%, UGIMA® 4598 contains less than 5% martensite. (See the chart on the right side of the material page)

General corrosion: General corrosion is defined as uniform corrosion of the entire surface; it is particularly found in mineral acid media such as sulphuric acid or phosphoric acid. The applications concerned are those of the chemical industry where the 316 family is sometimes used. This corrosion can be expressed as an annual thickness loss. In our laboratory, experiments carried out in sulphuric acid at a concentration of 2 moles/litre and at 23°C indicated that the corrosion rate of UGIMA® 4598 is three times higher than that of UGIMA® 4404, the grade for which the usual thickness loss limit of 1 mm/year is reached in this environment after approximately three months. The use of UGIMA® 4598 for this type of application must therefore be subject to a thorough examination.

Localised corrosion: Localised corrosion is mainly initiated on the surface by chloride ions (found in drinking water, seawater, de-icing salts, chlorinated cleaning products, etc.).

Pitting corrosion: Pitting corrosion resistance can be assessed by measuring the pitting potential in our laboratory (test standardised to ISO 15158).

The ISO 9227 neutral salt spray test was also applied to bars with drawn and turned surface finishes: after 1000 hours of testing, the surfaces of UGIMA® 4598 and UGIMA® 4404 bars are identical. Agricultural and food industry applications can be envisaged for UGIMA® 4598; however, it is not recommended for use in applications in the vicinity of the sea. (See the chart on the right side of the material page)

Crevice corrosion: In acid environments, i.e. environments with a pH between 1 and 4 and which contain chloride ions, the use of UGIMA® 4598 must be limited: under such conditions, the pitting potential of UGIMA® 4598 is effectively less than that of UGIMA® 4404. The passive film on UGIMA® 4598 is chemically dissolved for pH less than 3.5, whereas UGIMA® 4404 retains its passive film to a pH limit of 2.5.

Thanks to the addition of Cu and S and to the UGIMA® manufacturing process, UGIMA® 4598 exhibits machinability levels that are significantly better than those of UGIMA® 4404HM, as a result of a reduction in tool wear under identical cutting conditions and an improvement in chip breakability. Its machinability is even better than that of UGIMA® 4307HM, due mainly to its greatly superior chip breakability.

Machinability of bars at high temperature:

Turning: For turning, the tests performed at Ugitech's Research Centre were used to quantify these improvements (see the tables below). The improvement in terms of productivity for equivalent tool wear is almost 30% compared with UGIMA® 4404HM, which gives UGIMA® 4598 a slightly higher productivity rate than that of UGIMA® 4307HM. In terms of chip breakability, the improvement is even more significant, since the gap with UGIMA® 4404HM widens as it does with UGIMA® 4307HM (13 and 11 additional chip breaking conditions out of respectively 56 tested at different cutting feed rates and depths).

Drilling: For drilling, the very significant improvement in chip breakability already noted for turning gives UGIMA® 4598 far better machinability than that of UGIMA® 4404HM, with an increase of 50% to 80% in the potential productivity rates expressed in maximum chip flow rates * (see the table on the right side of the material page).

Machinability of bars at cold temperatures for screw machining:

Turning: For a rough turning operation, the improvement in productivity for equivalent tool wear is 30%, compared with UGIMA® 4404HM (see the table right side of the material page). For finish turning, UGIMA® 4598 reached the screw machine limits in terms of bar rotational speed (8000 rpm), giving an increase in productivity of at least 10% compared with UGIMA® 4404HM (and probably distinctly higher if the screw machine limits had not been achieved).

Drilling: Drilling with a coated carbide drill bit (one-piece or with an end-piece) increases the maximum chip flow rates by between 45% and 90% compared with those of UGIMA® 4404HM (see the chart on the right side of the material page).

Cross-cutting: For cross-cutting, the increase in productivity noted is 100% greater than that of UGIMA® 4404HM(see the chart on the right side of the material page).

Solution heat treatment (Solution annealing)

UGIMA® 4598 is solution-annealed prior to delivery. To restore the mechanical properties after hot or cold working, the same heat treatment can be performed. It involves maintaining a temperature of between 1020°C and 1120°C for a long period of time, followed by rapid cooling in air or water. This heat treatment, which is known as solution annealing, removes all trace of hardening, it gives the material its lowest mechanical properties (Rm and Rp0.2) and a high ductility, as well as optimum corrosion resistance.

Forging

UGIMA® 4598 can be forged at between 950°C and 1250°C, preferably between 1050°C and 1250°C where its forgeability is at maximum. As with all austenitic stainless steel grades, the force required to deform the metal is high (far higher than that required for carbon steels). Components can be cooled in air or water.

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UGIMA® 4598 can be welded by most arc welding processes (MIG/TIG, with or without filler metal, coated electrodes, plasma, etc.), by laser, resistance (spot or seam), friction or electron beam welding, etc. However, its strong tendency to thermal cracking requires the arc welding linear energies to be reduced as much as possible and the use of laser welding to be limited.

If filler wire is used, it is best to choose a UGIWELDTM 316LM type of wire that will give the welds a corrosion resistance at least equal to that of UGIMA® 4598.

For MIG welding, Argon (Ar) with a maximum of 2% to 5% CO₂ or O₂ should be used as shielding gas to prevent excessive oxidation of the weld seams obtained. Part of the Ar can be replaced with He (< 20%) and a few % of H₂ can be added, if required, depending on the intended applications. The addition of N₂ should be avoided, as it tends to increase the risk of thermal cracking in the weld metal zone.

For TIG welding, pure Argon should be used as a shielding gas to prevent premature oxidation of the tungsten electrode. In the same way as for MIG welding, part of the Ar can be replaced with He (< 20%) and a few % of H₂ can be added, if required, depending on the intended applications. The addition of N₂ should be avoided, as it tends to increase the risk of thermal cracking in the weld metal zone.